The present invention relates generally to an implantable intraluminal device. In its broadest aspect, the present invention relates to a means of attaching porous, non-textile polymeric membranes to a support structure, scaffold or framework. More particularly, the present invention relates to a composite intraluminal device including a support structure or framework, such as a stent, in combination with a porous membrane covering or liner.
It is well known to employ various endoprostheses for the treatment of diseases of various body vessels. One type of endoprostheses is commonly referred to as a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures or aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel. Often, stents may be used in conjunction with a graft with provides additional support for blood flow through weakened sections of the blood vessel.
Stents generally are open ended and are radially expandable between a generally unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded insertion diameter. Stents are often flexible in configuration, which allows them to be inserted through and conform to tortuous pathways in the blood vessels. The stent is generally inserted in a radially compressed state and expanded either through a self-expanding mechanism, or through the use of balloon catheters. For example, various stent constructions and their method of deployment are shown in U.S. Pat. No. 4,503,569 to Dotter; U.S. Pat. No. 4,733,665 to Palmaz; U.S. Pat. No. 4,856,561 to Hillstead; U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 4,732,152 to Wallsten and U.S. Pat. No. 4,886,062 to Wiktor. Published PCT Application No. PCT/US 95/08975, based on U.S. priority applications U.S. Ser. Nos. 08/282,181 and 08/457,354, also discloses a tubular shaped stent which is inflatable by balloon and which shrinks minimally in the longitudinal direction during expansion. The foregoing PCT publication and its U.S. priority applications, and the aforementioned U.S. patents are incorporated herein by reference. Additionally, published PCT Application WO 96/26689, entitled xe2x80x9cImproved Longitudinally Flexible Expandable Stentxe2x80x9d and being based on U.S. priority application Ser. Nos. 08/396,569 filed Mar. 1, 1995 and Ser. No. 08/511,076 filed Aug. 3, 1995 also discloses stents useful in the present invention, both this PCT Application and its U.S. priority applications being incorporated by reference herein.
The attachment of stents to grafts for use in endovascular applications has generally been by means of sutures, cuffs or pockets in the graft which serve to house the stent. For example, U.S. Pat. No. 5,522,881 discloses cuffs on the exterior surface of the graft which serve as open pockets into which stents can be placed. It is known to attach stents to grafts using sutures. For the most part, grafts which are used in combination with stents as composite device have been made from textile materials, which are woven, knitted or braided.
Composite devices made from stents and films have been disclosed in the art. For example, U.S. Pat. No. 5,123,916 to Lee describes an expandable intraluminal vascular graft which includes concentric cylindrical tubes having a plurality of scaffold members mounted therebetween. The scaffold members are expandable, ring-like and provide circumferential rigidity to the graft.
U.S. Pat. No. 5,383,926 to Lock, et al. describes a radially expandable endoprosthesis which comprises an elongated sleeve member in which the radially outward expansion of the sleeve is limited by connecting strips. These strips are selectively removable to allow further outward expansion. The sleeve can be C-shaped in cross-section to allow for further expanded growth. The sleeve member generally has an open wall structure such as those typical of wire mesh tubing or slotted tubing. An expandable sheet material may be disposed across the open region of the C-shaped sleeve member and may be formed of Goritex(copyright).
U.S. Pat. No. 5,389,106 to Tower discloses an impermeable expandable intravascular stent. An impermeable deformable membrane interconnects portions of a distensible frame to form an impermeable exterior wall to the frame. The membrane is formed of a synthetic non-latex, non-vinyl polymer and the frame is made from a fine wire of annealed platinum. The distensible frame may be an expandable stent and the membrane is a hypoallergenic biologically inert material that is free of latex rubber proteins. The membrane should be impermeable and have the properties of elasticity, distensibility and barrier protection. No specific classes of materials are mentioned except the product name Tactylon(copyright). The impermeable membrane is attached to the stent by dipping the stent into the polymer solution of the membrane and subsequently drying the device to remove the solvent. The stent is imbedded within the membrane surface.
With respect to grafts made from extruded materials such as ePTFE, the use of sutures to attach such grafts encounters problems of dealing with bleeding through suture holes, since these expanded fluoropolymer materials do not generally have the self-sealing capability of elastomeric materials. Additionally, ePTFE is inherently resistant to adhesive bonding and few biocompatible adhesives will bond to its surface. While this inherent surface characteristic of ePTFE has advantages because it imparts a natural anti-thrombogenic characteristic to the surface of grafts made therefrom, it has been heretofore difficult to attach stents to grafts made from ePTFE without encountering the foregoing problems. The present invention seeks to overcome difficulties of attaching ePTFE material to a stent by using an anchoring material which can be carried into and entrapped in the porous surface of ePTFE.
In certain applications, it is necessary to protect against excessive cell growth through the stent (intimal hypoplasia), as well as thrombus formation and plaque buildup in the vascular system. In the bile or urogenital tract regions, tumor growth is also of concern. Additionally, arterial build-up of plaque and other debris can become dislodged from the vessel surface during or subsequent to implantation of the stent. To prevent such occurrences, the use of a cover or liner in combination with an ePTFE stent has been suggested by the co-pending U.S. application Ser. No. 09/691,782 filed concurrently herewith and entitled xe2x80x9cImproved Covered Stentxe2x80x9d. This copending application describes the use of unsintered ePTFE as a cover or liner used for a radially expandable stent. This co-pending application is herein incorporated by reference. In the present application, a means of attaching such a cover or liner to a stent is provided.
In one embodiment of the invention, a support member/membrane composite device is provided, which device includes a support structure such as a radially expandable stent, a porous polymeric non-textile membrane adjacent to said support structure to define an interface therebetween; and a thermoplastic anchor means attached to and extending from said stent into said porous polymeric non-textile membrane at said interface to anchor the membrane to the support structure. The porous polymeric non-textile membrane may be selected from a variety of extruded materials such as ePTFE, polyurethane, polyimides and the like. The support structure can be essentially any medical device which is useful in or on the body. More preferably, the support structure is designed for use in the body, such as in intraluminal applications. Most preferably the support structure takes the form of a radially expandable stent.
The radially expandable stent may be chosen from a wide variety of stent materials and configurations. For example, the stent may be self-expandable, balloon expandable or made from a memory alloy, the configuration of which can be controlled by temperature. A thermoplastic anchoring material is attached to the stent and penetrates into the porous surface of the membrane. Penetration is accomplished without deleteriously interfering with the structural integrity of the membrane by dissolving a portion of the anchoring material at the support structure/membrane interface such that the dissolved material penetrates the pores of the membrane. The solvent is then removed, leaving the anchoring material to resolidify and form an anchoring means within the microporous membrane structure.
The support structure may be completely covered by a conformal coating of the anchoring material or it can be coated at selected, predetermined portions of the support structure which contact the membrane. For example, if the support structure is a stent, the stent may be completely or partially covered by the anchoring material.
The present invention further relates to a method of making an implantable support structure/membrane composite device, and preferably a tubular device, which includes the steps of providing a support structure; coating at least a portion of said support structure with a thermoplastic anchoring material; and positioning a biocompatible porous non-textile polymeric membrane in intimate contact with said anchoring material to form an interface therebetween. Further, this method includes the steps of dissolving with a suitable solvent at least a portion of said anchoring material at the support structure/membrane interface to cause penetration of said anchoring material into the porous membrane; and removing the solvent to allow resolidification of the anchoring material within the porous membrane, thereby anchoring said support structure to said porous membrane. In a preferred embodiment, the support structure is an expandable structure for intraluminal applications and most preferably a radially expandable stent.